In the title isoquinolinedione derivative, C(16)H(16)N(2)O(4), the piperidine ring in the tetra-hydro-isoquinoline unit adopts a half-boat conformation. The essentially planar oxazole ring [maximum deviation = 0.004 (2) Å] is inclined at a dihedral angle of 36.00 (8)° to the tetra-hydro-isoquinoline unit. In the crystal structure, pairs of inter-molecular C-H⋯O and O-H⋯N inter-actions link the mol-ecules into chains incorporating R(2) (2)(9) ring motifs. Two neighbouring chains are further inter-connected by inter-molecular C-H⋯O inter-actions into chains two mol-ecules wide along the a axis.